ON THE TREATMENT AND UTILIZATION OF SEAVAGE. 185 



There is this, then, against the catchwater-system, that if the fields are 

 not underdrained the laud will become saturated with sewage, and the 

 effluent water wlU then pass off in an impure condition ; and not only so, 

 but the present example shows that after a second application the water 

 may (except as regards actual ammonia) contain a greater amount of solu- 

 ble impurities than it did before ; and, above all, the nitrogenous organic 

 matter (as indicated by the albumenoid ammonia) is not diminished, but 

 rather increased, in spite of the active growth going on in the month of July. 



The temperature of the effluent water from the first field was considerably 

 (41° Fahr.) hirjher than that of the sewage, and that from the second field 

 half a degree higher than that from the first, a sufficient proof that percola- 

 tion through the soil does not take place. 



It may seem almost sujierfluous for the Committee, after so many years 

 of general experience throughout the country, to argue in favour of the sub- 

 soil drainage of naturally heavy or naturallj^ wet land with impervious sub- 

 soil for the purposes of ordinary agriculture ; but some persons have strongly 

 and repeatedly called in question the necessity of draining land when ir- 

 rigated with, sewage ; and the two farms at Tunbridge Wells, to a great ex- 

 tent, and more especially the E-eigate Farm at Earlswood, have been ac- 

 tually laid out for sewage-irrigation on what may be called the " satura- 

 tion " principle ; so that it appears to the Committee desirable to call atten- 

 tion to the fact, that if drainage is necessary where no water is artificially 

 supplied to the soil, it cannot be less necessary after an addition to the rain- 

 fall of 100 or 200 per cent. But a comparison of the analyses of different 

 samples of effluent waters which have been taken by the Committee from 

 open ditches into which effluent water was overflowing off saturated land, 

 and from subsoil-drains into which effluent water was intermittently perco- 

 lating through several feet of soil, suggests grave doubts whether effluent 

 water ought ever to be permitted to escape before it has percolated through 

 the soil. 



Section 1Y. — The Phosplmte Process. 



A Member of the Committee was present at an experiment which was 

 performed with the phosiihate process of Messrs. Forbes and Price at 

 Tottenham on March 25th, 1871. His description of the experiment is as 

 follows : — 



The Tottenham sewage, after passing through some depositing tanks which 

 had been constriicted for the lime-process, was pumped up, at the rate of 

 about 800 or 1000 gallons per minute (as stated), along a carrier into a tank 

 100 yards long and of gradually increasing breadth. This tank took three 

 hours to fill. 



As the sewage passed along the above mentioned carrier, the chemicals 

 were mixed with it in the following way : — 



Two boxes were placed over the carrier, one a few yards further along it 

 than the other; the first contained the phosphate mixture, and the second 

 milk of lime. Men were continually stirring the contents of each box, 

 w'hich were allowed to run continuously into the sewage as it passed xmder- 

 ncath the boxes. 



The phosphate mixture was stated to be made by powdering the native 

 phosphate of alumina, mixing it with sulphuric acid in the proportion of a 

 ton of phosphate to from 12 to 13 cwt. of the acid, and dissolving the mass 

 in water. 



